9mm Luger
no. nor can you fit a 40 cal shell into a 9mm chamber...............
Clip system darts
The Walther P99 in 9mm Parabellum has 2 standard size magazines- one holds 10 cartridges, the other 15. PS- BULLET is the part of the cartridge that comes out of the barrel. Magazine capacities are in cartridges, not bullets.
No. It depends on the make and model of your 9mm and what kind of magazine it was designed to take. In the past automatic pistols each had their own magazine and they were very seldom interchangeable. Today there is more interchangeability, but there is as yet no universal magazine that will fit into every 9mm.
9mm and 380 both use bullets with a diameter of .355. However, the cases are a different size. .380 is also known as .380 auto, 9mm Kurtz, 9mm Corto, 9mm short or 9x17. 9mm typically refers to 9x19mm also known as 9mm Parabellum or 9mm Luger. You cannot fire a 9mm Parabellum cartridge from a .380 handgun. The 9mm cartridge will not fit into the chamber of the gun. However, if you were to pull the bullet out of the .380 case and put it into a 9mm Para case the resulting cartridge will work just fine.
Streamline foam darts with drum/clip. Or: if you are able to, manually load any other dart that can fit in the barrel, BUT this is not recommended.
Assuming that a Williams PPK is a copy of a Walther PPK, and assuming that it is marked as .380 caliber or 9mm Kurz, and assuming you mean 9x19mm or 9mm Luger, no. You may get the cartridge to fit, but you should not try to fire it. It may even possibly fire, but will probably damage the gun and possibly the shooter.
any Nerf manufactured bullets will fit.
No
No
As a general rule, no.